The Mark of Cain documents the fading art form and “language” of Russian criminal tattoos, formerly a forbidden topic in Russia. The now vanishing practice is seen as reflecting the transition of the broader Russian society. Filmed in some of Russia’s most notorious prisons, including the fabled White Swan, the interviews with prisoners, guards, and criminologists reveal the secret language of “The Zone” and “The Code of Thieves” (Vor v zakone).